You can think of a category as a container for subcategories. Because documents and questionnaires can only be assigned to subcategories, each top-level category you create must contain at least one subcategory before it is useful for categorizing documents/questionnaires.
To add a top-level category,
Note: You can assign the category to additional sites later in the process.
Name. This is the name that appears in the category list. This name must be unique across all sites.
Reference ID. By default, the reference ID is auto-filled with the category name. You can change the reference ID, but be aware that it must be unique.
(Optional) Category Owner. If you want to assign someone to manage this category (to add and maintain subcategories), for Category Owner, click a user name. (See Assigning System Permissions for details on assigning a user as a category owner.)
Sites.
Selection Type. This property determines whether document owners can assign a document/questionnaire to just one subcategory under this category or to more than one. The default setting is Single.
(Optional) Constraints.
(Optional) Description. Add a description to explain what the category is for and the type of subcategories it should contain.